1. Technical Field
The present invention relates to a photosensitive resin composition suitable for forming a light shielding film for an image display device such as a liquid crystal display (hereinafter, referred to as “LCD”).
2. Description of the Related Art
A liquid crystal display (LCD) displays an image using optical anisotropy and birefringence of liquid crystal molecules. When an electric field is applied to a liquid crystal display (LCD), the liquid crystal alignment changes, which causes the light transmission characteristics to change.
Generally, in a liquid crystal display (LCD), when two substrates, which are each provided with electrodes to form an electric field, are disposed such that the electrodes face each other, a liquid crystal material is charged between the two substrates and then a voltage is applied to the electrodes to form an electric field. In this case, liquid crystal molecules move under the influence of the electric field and their light transmission changes, thereby displaying an image.
For example, a widely-used thin film transistor liquid crystal display (TFT-LCD) includes: a lower substrate, called an array substrate, on which thin film transistors and pixel electrodes are arranged; an upper substrate, called a color filter substrate, which is made of glass or plastic and which includes a black matrix and which also includes red, green and blue colored layers formed on the upper substrate; an overcoat having a thickness of 1˜3 um and formed on the three colored layers, the overcoat being made of polyimide, polyacrylate, polyurethane or the like and serving to protect a color filter and maintain surface flatness, and a transparent conductive layer made of indium tin oxide (ITO) and formed on the overcoat, a voltage for driving liquid crystals being applied to the transparent conductive layer; and liquid crystals charged between the lower substrate and the upper substrate. Here, each of the lower and upper substrates is provided on both sides thereof with a polarizing plate that polarizes visible light (natural light). In the thin film transistor liquid crystal display (TFT-LCD), a voltage is applied to a TFT gate including pixels by an external circuit to turn on the TFT such that zero-phase voltage can be input to liquid crystals. Then, zero-phase voltage is applied thereto to store image information in the liquid crystals, and then the TFT turns off to keep electric charges stored in a liquid crystal charger and an auxiliary charger, thus displaying an image for a predetermined amount of time. When voltage is applied to the liquid crystals, the alignment of the liquid crystals changes, at which time, when light penetrates these liquid crystals, the light is diffracted. This diffracted light penetrates the polarizing plate, thus obtaining desired images.
Recently, efforts to increase the aperture ratio, simplify a manufacturing process and decrease a manufacturing cost by forming a color filter on a lower substrate, that is, an array substrate, not an upper substrate, that is, a color filter substrate, have been made.
Even though considering such a structural change in the TFT-LCD, a color filter is generally formed by dyeing, spraying, electrodepositing, ink-jet printing or the like. In particular, a technology of forming a color filter by ink-jet printing is advantageous in that it can simplify processing and reduce costs. However, the color filters formed by ink-jet printing are problematic because they cannot be formed in a uniform manner in a glass substrate or a liquid crystal display cell. The reason for this is because the nozzles of an ink-jet printer head discharge different amounts of ink. When the amounts of ink discharged by the nozzles of an ink-jet printer head are different from each other, there is a problem in that the amount of ink charged in each pixel region changes, and thus the color filters can be recognized as mottles. Further, when a light-shielding pattern, that is, a space corresponding to a pixel region defined by a black matrix, is charged with color ink, the color ink can be swollen in the form of a dome by the repulsion between the light-shielding pattern and the color ink and the surface tension of the color ink. Owing to the color ink charged in the space in the form of a dome, the thickness of the color filter formed at the center of a pixel region is different from the thickness of the color filter formed at the edge of the pixel region, thus causing color aberration. Therefore, due to the poor uniformity of the color filter attributable to these factors, display quality finally deteriorates.